JP4374602B2 - Heavy metal immobilizing agent and waste treatment method thereof - Google Patents

Description

  The present invention relates to a heavy metal immobilizing agent for waste containing harmful heavy metals such as fly ash, incinerated ash, or molten fly ash generated in a waste incineration plant, and a waste treatment method using the heavy metal immobilizing agent. .

  Incinerated ash and fly ash generated when incinerating municipal waste and industrial waste, or molten secondary fly ash generated when further melting the incinerated ash, etc., contains harmful heavy metals such as lead and cadmium. When these wastes are disposed of in landfills, chemical treatment with chelating agents or amorphous aluminum hydroxide is often performed in order not to elute harmful heavy metals from the wastes. As this chelating agent, a dithiocarbamic acid type drug, a piperazine type drug, etc. are known (patent documents 1 and 2).

  The conventional waste treatment method using a chelating agent is based on the fact that harmful heavy metals are re-eluted with the decomposition of the chelating agent after landfill treatment, or the heavy metals are reversibly dissociated from the heavy metal and the chelate compound. It has been pointed out that re-elution occurs.

  On the other hand, heavy metal treatment with amorphous aluminum hydroxide (Patent Document 3) is effective depending on the target ash species, but in the treatment of ash fly ash with high alkali strength, a large amount of chemical addition rate is required. In other words, there is a problem that the amount of final waste increases and the processing cost increases.

  In addition to the above treatment method, a waste treatment method using water glass (Patent Document 4), a treatment method using a heat treated product of calcium sulfoaluminate hydrate (Patent Document 5), a soluble sulfur-containing alkali A number of waste treatment methods have been proposed, such as a treatment method using an aqueous solution (Patent Document 6) and a chemical mixed with blast furnace granulated slag and thiourea (Patent Document 7).

  However, in the waste treatment method using water glass, water glass is consumed immediately by forming a compound such as CSH compound with the calcium component present in the waste, so it is harmful unless a considerable amount of water glass is used. It is difficult to immobilize heavy metals effectively and reliably, especially when the concentration of calcium present in the waste is high, a considerable amount of water glass is required, increasing the amount of final waste and increasing the processing cost. There is a problem of becoming.

  In addition, waste treatment with a calcium sulfoaluminate compound requires high-temperature treatment at 500 ° C. in order to produce a calcium sulfoaluminate compound, and this synthesis requires a considerable amount of energy, so it is not suitable for waste treatment. In addition, calcium sulfoaluminate compounds typified by ettringite have a large crystal structure, and it has been pointed out that heavy metals leak from gaps between crystals. There is a problem that the amount of use becomes enormous, which also increases the amount of final waste and increases the processing cost.

  In addition, treatment with an alkaline aqueous solution containing soluble sulfur typified by sodium sulfide is a method for stabilizing sulfurization of harmful heavy metals, and it is known that its stability is high, but the drug itself is expensive, There is a problem that the processing cost is increased overall.

  Furthermore, a treatment agent in which thiourea is added to ground granulated blast furnace slag has been proposed, but thiourea has not been put into practical use because it is highly toxic in acute toxicity and carcinogenic. As described above, various processing methods have been proposed in the past. However, there is much room for improvement in order to perform processing reliably and simply, more inexpensively and safely.

Moreover, as a reality, the heavy metal fixing agent for waste containing toxic heavy metals such as fly ash, incineration ash, or molten fly ash generated at the waste incineration plant is most typically amorphous aluminum hydroxide. Water glass, calcium sulfoaluminate hydrate, soluble sulfur-containing alkaline aqueous solution, and chemicals mixed with ground granulated blast furnace slag and thiourea have been proposed in the literature, but there are few or no examples. It is. Moreover, the amorphous aluminum hydroxide generally used has a limit in the treatment effect with respect to refuse incineration ash and incineration fly ash, and improvement of these chemicals is strongly demanded.
JP-A-9-75892 Japanese Patent No. 2862813 JP-A-9-47740 Japanese Patent Laid-Open No. 9-308771 JP 2001-70926 A Japanese Patent Laid-Open No. 11-123374 Japanese Patent Laid-Open No. 10-192813 Japanese Patent Publication No. 52-39622 Japanese Patent Publication No.51-22472 Japanese National Patent Publication No. 11-501574 JP 2004-321887 A

  The present invention solves the above-mentioned problems of the conventional method, immobilizes heavy heavy metals in the long term, can prevent re-elution, and can achieve the immobilization of heavy metals with a small addition rate A waste treatment method using the agent and the immobilizing material is provided.

The present invention relates to a heavy metal immobilizing agent and a waste treatment method that have solved the above-described problems with the following configurations.
[1] An immobilizing agent for fixing heavy metals in waste, the content of dosonite NaAlCO ₃ (OH) ₂ is 70% by weight or more, and 15 to 50 parts by weight of water per 100 parts by weight of waste The aluminum component dissociated from dosonite reacts with the calcium component in the waste to form a calcium-aluminum compound, and the carbonate ion component or bicarbonate ion component dissociated from the dosonite is used in a water-soluble atmosphere of dosonite. A heavy metal immobilizing agent characterized by reacting with a heavy metal and stabilizing by carbonation.
[2] (a) 2 to 5 parts by weight based on 100 parts by weight of municipal waste incineration ash, (b) 3 to 15 parts by weight based on 100 parts by weight of municipal waste incineration fly ash, or (c) The heavy metal immobilizing agent according to claim 1, which is used by blending 5 to 15 parts by weight with respect to 100 parts by weight of molten secondary fly ash.
[3] The above [1] or the above containing one or more of a neutralizing agent, an adsorbent, a sulfurizing agent, a carbonating agent, a mineral structure forming material, a phosphoric acid compound, a solidifying agent, and a chelating agent together with dosonite [2] The heavy metal immobilizing agent according to any one of [2].
[4] For a waste containing heavy metal, a fixing agent having a content of 70% by weight or more of dosonite NaAlCO ₃ (OH) ₂ is added to a water content of 15 to 50 parts by weight with respect to 100 parts by weight of the waste. And (b) 100 to 100 parts by weight of municipal waste incineration ash, and (b) 100 parts by weight of municipal waste incineration fly ash. 3 to 15 parts by weight, or (c) 5 to 15 parts by weight based on 100 parts by weight of molten secondary fly ash, and the aluminum component dissociated from dosonite is combined with the calcium component in the waste. A waste treatment method characterized by reacting to form a calcium-aluminum compound, and a carbonate ion component or a hydrogen carbonate ion component dissociated from dosonite reacts with a heavy metal to stabilize by carbonation.

  Since the heavy metal immobilizing agent of the present invention is mainly composed of dawsonite, it is excellent in the effect of immobilizing heavy metals, and can be used to immobilize heavy metals such as lead with a relatively small amount used, and the elution amount of heavy metals Can be reduced below the landfill elution standard.

  Furthermore, the heavy metal immobilizing agent of the present invention is used in a wet state below the water content in the paste state when added to waste, and specifically, for example, the immobilizing agent of the present invention together with a small amount of water. In addition to waste, it can be used in a wet state such as clay or slightly hardened paste, so there is no need to add a large amount of water to the waste to make a suspension, and precipitation equipment such as thickeners Etc. are unnecessary. As described above, according to the heavy metal solidifying agent of the present invention, since the dry treatment can be performed, the post-treatment is easy, and it is possible to easily carry out without requiring a large facility.

Hereinafter, the present invention will be specifically described based on embodiments.
The heavy metal immobilizing agent of the present invention is an immobilizing agent for immobilizing heavy metals in waste, and the content of dawsonite NaAlCO ₃ (OH) ₂ is 70% by weight or more, and is 15% relative to 100 parts by weight of waste. Carbonate component dissociated from dosonite, which is used under a water content of ˜50 parts by weight and water-soluble atmosphere of dosonite, and the aluminum component dissociated from dosonite reacts with the calcium component in the waste to form a calcium-aluminum compound. It is a heavy metal immobilizing agent characterized in that a bicarbonate ion component reacts with a heavy metal to stabilize by carbonation .

Dowsonite NaAlCO ₃ (OH) ₂ , which is the main component of the heavy metal fixing agent according to the present invention, is produced as an aluminum-containing ore, and synthetic dawsonite is produced under general industrial production conditions. Since synthetic dosonite is porous, it is conventionally used as a plastic additive to absorb harmful gases (Patent Document 8), heavy metal adsorbents in liquids, adsorbents of malodorous components, drainage, smoke, It is used as a remover that adsorbs toxic components in exhaust gas (Patent Document 9).

  However, the use of dosonite in the liquid phase is completely different from the dry use in the solid state or in the wet state, so the fly ash, incineration ash, or molten fly ash generated at the waste incineration plant is completely different. For example, it is not used as a dry heavy metal fixing agent from a wet powder having a moisture content of 50% by weight or less to a clay state or a paste state.

  The heavy metal-containing waste in which the heavy metal immobilizing agent of the present invention is used includes incineration ash discharged from municipal waste or industrial waste incineration plants, and flying collected by dust collection equipment such as bag filters and electric dust collectors. Examples include ash, soot and fly ash such as molten secondary fly ash generated when further melted. In addition, the burning husk, soot dust, etc. containing a heavy metal should just be sufficient, and it is not restricted to the said fly ash.

  These dusts, fly ash, etc. are very water-absorbing. For example, when the amount of added water is about 15 to 20% by weight, the powdery state is slightly wet and the amount of added water is about 35 to 50% by weight. Is a relatively hard clay, and when the water content is 20 to 35% by weight, it is in an intermediate state from powder to clay. When the heavy metal immobilizing agent of the present invention is added to the waste, such as dust and fly ash, in a wet state below the moisture content in the paste state, specifically, It is used in a solid state in a clay state from a wet powder of 50% by weight or less.

  Conventionally, a heavy metal ion scavenger made of a mixture of alkali silicate and hydroxy carbonate is known, and dawsonite has been exemplified as a kind of hydroxy carbonate. It is used to capture heavy metal ions in the liquid and is not intended for use in solid waste. Moreover, it contains an alkali silicate as an essential component in addition to the hydroxy carbonate, and is different from the heavy metal immobilizing agent of the present invention in usage and the like (Patent Document 10).

  In addition, a method for modifying contaminated soil has been proposed for adsorption and immobilization of fluorine, arsenic, and harmful metals with hydrotalcite compounds, which is a kind of aluminum compound. This method relates to fluorine ions and oxide anions. Therefore, the field and object are different from the present invention (Patent Document 11). In addition, as shown in the treatment effect described later as a comparative example, hydrotalcite compounds are used for immobilizing heavy metals in waste containing harmful heavy metals such as fly ash, incineration ash, or molten fly ash generated in a garbage incineration plant. It is unsuitable as an agent.

  Incineration ash discharged from municipal waste or industrial waste incineration plants and fly ash collected by dust collection equipment such as bag filters and electric dust collectors are mostly strongly alkaline, or are generated when further melted. Most of the molten secondary fly ash which shows is weakly acidic. Moreover, any waste contains a large amount of calcium components.

When the fixing agent of the present invention is used for the above dust, fly ash, etc., the dosonite shows water solubility in a strong alkaline atmosphere and a weakly acidic atmosphere, and from the dissolved dosonite, an aluminum component and a carbonate ion component or hydrogen carbonate. Each of the ionic components dissociates, and the dissociated and dissolved aluminum component quickly forms a stable calcium-aluminum compound with a calcium component present in a large amount in the waste, and has a neutralizing action and has a mineral structure such as ettringite. A precursor is formed, and the formation of a stable structure is promoted as the processing time elapses. Furthermore, the carbonate ion component or the hydrogen carbonate ion component dissociated and dissolved from dawsonite promotes the stabilization of carbonation of harmful heavy metals such as lead.

  The heavy metal immobilizing agent of the present invention may be dawsonite alone, but may contain other components together with dawsonite depending on the properties of the waste. Specifically, for example, neutralizers represented by sulfate bands, adsorbents represented by aluminosilicate compounds, sulfurizing agents represented by sodium sulfide, and the like, represented by sodium carbonate and sodium hydrogen carbonate. Carbonation agent, mineral structure forming material such as ettringite by combination with other components typified by aluminum hydroxide, phosphate compound that promotes phosphate mineral formation, solidifying agent typified by Portland cement, etc. You may contain a powder chelating agent etc.

  For example, when the waste exhibits extremely strong alkalinity, it is also effective to use a neutralizing agent sulfate band together with dawsonite. Specifically, it is effective to use a sulfuric acid band as a neutralizing agent in combination with a strong alkaline waste in which the calcium component contained in the waste exceeds 50% by weight in terms of calcium oxide.

  In addition to this, the fixing agent of the present invention is combined with an adsorbent typified by an aluminosilicate compound, a carbonating agent typified by sodium carbonate or sodium hydrogen carbonate, and other components typified by aluminum hydroxide. May be mixed with a mineral structure forming material such as ettringite and a phosphate compound that promotes the formation of phosphate mineral. These compounds are relatively inexpensive, and the blending amount may be determined based on the balance with the effect of use.

  Moreover, you may mix the sulfiding agent represented by sodium sulfide and potassium sulfide with the fixing agent of this invention. However, these sulfiding agents themselves are very expensive drugs, resulting in an increase in the unit price of the mixed drug and are not economical.

  In the fixing agent of the present invention, the content of the main component dosonite is suitably 70% by weight or more. If the content of dawsonite is less than 70% by weight, the effect of immobilizing heavy metal of dawsonite is not sufficiently exhibited, and a large amount of addition is required for the object to be treated, which is not economical.

  The immobilizing agent of the present invention is generated when incinerated ash discharged from municipal waste or industrial waste incineration plants, fly ash collected by dust collection equipment such as bag filters and electric dust collectors, or further melted. When the molten secondary fly ash is added to these wastes, it is used in a wet state below the water content in the paste state. Specifically, for example, by adding the fixing agent of the present invention to a waste together with a small amount of water, in a wet state with a small amount of water such as a wet powder, clay, or a slightly hard paste. used. It is used in such a wet state with a small amount of water, and a dry process different from the liquid phase state can be performed. If the water content is larger than this, it is not preferable because it is not suitable for dry treatment.

  Specifically, for example, it is used under a moisture amount of 50% by weight or less, preferably 20 to 45% by weight. By adding the immobilizing agent of the present invention to the dust / fly ash containing heavy metal, and kneading and kneading so as to be in the state of the moisture content, incineration ash, fly ash, molten secondary The heavy metal contained in the fly ash is fixed, the fixing performance of heavy metals is further enhanced with the increase in the number of curing days, and the fixing property can be maintained for a long time.

  The amount of the fixing agent of the present invention is appropriately selected depending on the properties of the waste, but when the object to be treated is municipal waste incineration ash, it is usually 2 to 5 parts by weight with respect to 100 parts by weight of incineration ash. It is preferable to mix, and when the object to be treated is municipal waste incineration fly ash, it is usually preferable to add 3 to 15 parts by weight with respect to 100 parts by weight of incineration fly ash, and when the object to be treated is melt-treated. In the case of the molten secondary fly ash that is generated, it is usually preferable to blend 5 to 15 parts by weight with respect to 100 parts by weight of the molten secondary fly ash.

  If the amount of the fixing agent used is less than the above range, a sufficient effect cannot be obtained. For example, for lead, which is a toxic heavy metal, the landfill elution standard of 0.3 mg / liter may not be achieved. In addition, even if there is too much usage-amount of the fixing agent of this invention, although the heavy metal fixation effect is fully exhibited, it is not economical.

  As for the amount of water added, it is sufficient that when the immobilizing agent of the present invention is added, the wet state such as a wet powder state, a clay state, or a slightly hard paste state may be obtained. What is necessary is just to determine according to a kneading | mixing installation, and 15-50 weight part normally with respect to 100 weight part of waste materials, Preferably 20-45 weight part is suitable.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to the following examples. The heavy metal fixing agent shown in Table 1 was used. Fixing agents (E) (F) (G) (H) (I) are comparative examples. Table 2 shows the types of waste used and the components of each waste.

[Test method: 1]
The heavy metal fixing chemicals and water shown in Table 1 were added to the wastes shown in Table 2, mixed uniformly, and kneaded to form clay. This was cured for 1 day, then cured for 30 days, and an elution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. The processed product for 1-day curing was stored indoors, and the processed product for 30-day curing was stored outdoors and then subjected to a dissolution test. In all samples, the water content was 40% by weight of the weight of the waste to be treated. The test results are shown in Table 3. In addition, the results of dissolution tests conducted by the Environmental Agency Notification No. 13 test in 1973 for wastes without added immobilizing agents are also shown as reference examples.

  As for waste (1), as shown in Examples 1 to 3, those using the immobilizing agents A and C of the present invention have an elution amount of Pb of 2 to 5% by weight with respect to the waste. It was not detected and an excellent immobilization effect was confirmed. On the other hand, in Comparative Example 1 using the conventional amorphous aluminum hydroxide fixing agent F, elution of Pb was observed after 1 day of curing even in the 5% by weight addition treatment, and it was confirmed that the heavy metal immobilization performance was low. It was done. From this comparison, it can be seen that the immobilizing agent mainly composed of dawsonite of the present invention has better immobilizing performance than conventional aluminum compounds. In addition, in the case of using the organic drug fixing agent I, Pb was eluted after 30 days of curing, and it was observed that Pb was re-eluted.

  Moreover, it was confirmed that the immobilizing agent G using carbonate ion type hydrotalcite, which is often regarded as a compound similar to dawsonite, could not immobilize Pb which is a harmful heavy metal (Comparative Example 2). Similarly, it was confirmed that the fixing agent H, which is a so-called carbonating agent, could not fix Pb (Comparative Example 3).

  As is clear from the comparison with Examples 1 to 3 and Comparative Examples 2 to 3 of the present invention, the immobilizing agent of the present invention mainly composed of dawsonite has a performance exceeding that of conventional aluminum heavy metal immobilizing agents. Furthermore, it can be seen that the carbonate ion-type hydrotalcite and the carbonating agent, which are often considered to be similar compounds, exhibit the effects that the carbonation agent does not have.

  As for waste (2), as shown in Examples 4 to 6, Pb was slightly eluted after 1 day of curing in Example 4 using the immobilizing agent A of the present invention. The value is below, and elution of Pb is not detected after 30 days. In Examples 5 to 6, elution of Pb was not detected in both of the fixing agents A and B, and an excellent fixing effect was confirmed.

  On the other hand, those using the fixing agents E and F have a high Pb elution amount after 1 day of curing (Comparative Examples 5 and 6). In addition, in the case of using the immobilizing agent I, Pb was eluted after 30 days of curing, and it was observed that Pb was re-eluted here (Comparative Example 9). Further, in Comparative Examples 7 and 8, it was confirmed again that the carbonate ion type hydrotalcite and the carbonating agent do not have the heavy metal immobilization performance of dust.

  Regarding waste (3), as shown in Examples 7 to 9, those using the immobilizing agents A and B of the present invention are slightly less than the landfill elution standard, although Pb elutes slightly after one day of curing. No elution of Pb is detected after 30 days. In addition, in the case of using the immobilizing agent D, the elution of Pb is not observed even after 1 day and 30 days after curing.

  On the other hand, in Comparative Example 11 in which the fixing agent F was used, elution of Pb was observed after one day of curing despite the highest fixing agent addition rate to the waste. Further, in Comparative Example 12 using the immobilizing agent I, Pb was eluted after 30 days of curing, and it was observed that Pb was re-eluted.

  As for waste (4), as shown in Examples 10 to 13, in the case of using the fixing agents A, B and C of the present invention, Pb is eluted slightly after 1 day of curing. Pb elution is not detected after 30 days. In addition, in the case of using the immobilizing agent D, the elution of Pb is not observed even after 1 day and 30 days after curing.

  On the other hand, in Comparative Examples 13 to 14 using the immobilizing agent F, elution of Pb was observed after 1 day of curing, and elution of Pb was also observed after 30 days at a fixing agent addition rate comparable to that of the immobilizing agent of the present invention. (Comparative Example 14). Further, in Comparative Examples 15 to 16 using the immobilizing agent I, Pb was eluted after 30 days of curing, and it was observed that Pb was re-eluted.

  From the above results, according to the heavy metal immobilizing agent of the present invention, incineration ash discharged from municipal waste or industrial waste incineration plants, fly ash collected by dust collection equipment such as bag filters and electric dust collectors, Or, for waste containing toxic heavy metals such as molten secondary fly ash generated during further melting treatment, toxic heavy metals can be fixed in the long term and re-elution can be prevented. It was confirmed that immobilization of heavy metals can be achieved. Moreover, in the wastes (1) to (4), there was a case where elution of Cd, As, hexavalent Cr, etc. was observed before the chemical treatment, but any of the treated products using the fixing agent of the present invention The elution of Cd, Hg, As, Se, and hexavalent Cr was not detected and could be landfilled.

[Test method: 2]
For the fixing agent A shown in Table 1, which is a heavy metal fixing agent of the present invention, and the amorphous aluminum hydroxide fixing agent F, which is a conventional aluminum-based fixing agent as a comparative control, the comparison of the drug effect is as follows. We examined in detail. First, fixative and water are added to the waste (2) listed in Table 2 and mixed and kneaded uniformly. After curing for 1 day, the dissolution test is conducted according to the Environmental Agency Notification No. 13 test in 1973. Carried out. In all samples, the water content was 40% by weight of the weight of the waste to be treated. The test results are shown in Table 4 and FIGS.

  Addition of a fixing agent that satisfies the Pb standard value (0.3 mg / liter) of hazardous heavy metals when the treatment effect of fly ash, which is a specially managed waste, is treated with the heavy metal fixing agent When the ratio is compared, as shown in FIG. 1, the immobilizing agent comprising dawsonite of the present invention is almost equivalent to the conventional immobilizing agent amorphous aluminum hydroxide by adding about 1/3 amount. It can be seen that the effect of immobilizing heavy metals has been achieved, the amount used is much smaller than that of conventional drugs, and the immobilization performance has been dramatically improved.

  Furthermore, as shown in FIG. 2, when comparing the addition ratio to fly ash based on aluminum, which is the main element, among the fixing agents, the fixing agent made of dawsonite of the present invention is a conventional amorphous material. It can be seen that the addition of about 1/5 with respect to the quality aluminum hydroxide achieves substantially the same heavy metal immobilization effect, and has an excellent effect which is not expected at all from the conventional use amount.

The graph which shows the relationship between the addition rate of the fixing agent A and the fixing agent F with respect to a waste (2), and Pb elution amount. The graph which shows the relationship between Al addition rate in the fixing agent A and the fixing agent F with respect to a waste (2), and Pb elution amount.

Claims (4)

A fixing agent for fixing heavy metals in waste, the content of dosonite NaAlCO ₃ (OH) ₂ is 70% by weight or more, the water content of 15 to 50 parts by weight with respect to 100 parts by weight of waste and dosonite The aluminum component dissociated from dosonite reacts with the calcium component in the waste to form a calcium-aluminum compound, and the carbonate ion component or bicarbonate ion component dissociated from dosonite reacts with the heavy metal. And a heavy metal fixing agent characterized by being stabilized by carbonation.   (B) 2 to 5 parts by weight with respect to 100 parts by weight of municipal waste incineration ash, (b) 3 to 15 parts by weight with respect to 100 parts by weight of municipal waste incineration fly ash, or The heavy metal fixing agent according to claim 1, which is used by blending 5 to 15 parts by weight with respect to 100 parts by weight of the next fly ash.   Either 1 or 2 containing a neutralizer, an adsorbent, a sulfiding agent, a carbonating agent, a mineral structure forming material, a phosphoric acid compound, a solidifying agent, and a chelating agent together with dosonite. A heavy metal immobilizing agent described in the above. For a waste containing heavy metal, a fixing agent having a content of dosonite NaAlCO ₃ (OH) ₂ of 70% by weight or more, a water content of 15 to 50 parts by weight with respect to 100 parts by weight of the waste, and dosonite It is a treatment method used in a water-soluble atmosphere , and (b) 2 to 5 parts by weight is blended with respect to 100 parts by weight of municipal waste incineration ash; 15 parts by weight or (c) 5 to 15 parts by weight based on 100 parts by weight of molten secondary fly ash is used, and the aluminum component dissociated from dosonite reacts with the calcium component in the waste. A waste treatment method characterized by forming a calcium-aluminum compound and allowing a carbonate ion component or a hydrogen carbonate ion component dissociated from dawsonite to react with a heavy metal to stabilize by carbonation.

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